Longitudinal positioning apparatus use elongated elements, such as piston rods, spindles and the like, to move a positioning element. If the positioning element is driven by a spindle, the positioning element is coupled to a spindle nut which is located in a housing or a frame structure, to be non-rotatable with respect to the housing or frame, but longitudinally slidable thereon. The positioning element itself is coupled to the spindle nut.
Spindles which are very long should be supported along their length to prevent oscillations, bend-through, and the like. German Pat. No. 32 05 143 describes a linear positioning apparatus in which a spindle is located in a tubular, essentially rigid housing formed with a longitudinal slit. The housing retains bearing elements at both ends thereof, the spindle extending therethrough, and being coupled at one end to a drive motor. The positioning element itself extends through the slit in the housing, and is coupled to a spindle nut.
The linear positioning apparatus permits longitudinal movement of machine elements coupled to the positioning element and precisely positioning the machine element with respect to the housing, or a predetermined reference, by driving the spindle. The positioning speed, likewise, is readily controllable. The axial length of the spindle, in relation to its diameter, and in further relation to the maximum speed of the spindle, does not require radial support of the spindle intermediate the bearing ends at the end of the housing if the speed, diameter and length are matched and are below predetermined limits. If the spindle is extra long, or thin, however, or the speed increased, additional apparatus or devices are required in order to radially support the spindle in the region between the bearings at the ends of the housing and the spindle nut.
Radial support of spindles which are thin or are operated at high speed, and are of substantial length, is necessary to prevent bend-through of the spindle and, when driven, to prevent orbital movement about the longitudinal axis of the housing. Such movements, which may also be in the form of oscillations or vibrations, excessively stress the spindle, the spindle nut, the bearings, and, if excessive, may lead to damage of the housing itself. The length of the free regions of the spindle changes as the spindle nut changes its position with respect to the ends or another reference position of the housing. This requires that radial support elements must travel together with travel of the spindle nut in order to prevent interference with longitudinal movement of the spindle nut as the spindle is being driven.
Some structures used in actual arrangements use essentially ring-shaped support elements, threaded about the spindle, which are longitudinally guided and supported on the inner wall of the housing. Coupling elements are provided which permit the spindle nut to carry along the support elements during movement of the spindle nut. These coupling elements are longitudinally extending steel strips which connect the coupling elements with the spindle. The steel strips have dirrerent lengths for the respective support elements. The steel strips are slidable on the spindle nut. As the spindle nut travels in one direction, the leading side of the spindle nut collects the support elements at the front side thereof, and pushes the support elements along. At the same time, support elements at the trailing side--with respect to movement of the spindle nut --are likewise carried along. The support elements at the trailing side, however, will remain in the housing as the steel strips are being played out from the spindle nut, so that the spindle, in the distances determined by the length of the steel strips, will be radially supported. If the direction of movement of the spindle nut is then reversed, the previously leading support elements now become the support elements at the trailing side, and the process will reverse, with the previously trailing support elements being collected in front of the spindle, and the previously leading spindle nuts now trailing and being paid out in accordance with the length of the steel strips connecting the support elements to the spindle nut.
Two connecting strips are provided for each support element. The number of support elements, thus, is limited by the size of the apparatus and the space available to accomodate the steel strips. The maximum spacing of the support elements is determined by the length of the steel strips. Further, it may occur that upon longer travels of the spindle nut, the support elements will follow the spindle nut with spacing determined by the respective lengths of the steel strips. Consequently, in particularly long spindles, the space between the last support element, that is, the one that has the longest steel strips associated therewith, and the associated bearing flange may becone undesirably long, leaving a long non-supported region of the spindle.
The arrangement has an additional disadvantage, namely that the drive is preferentially useful only for essentially horizontal drive; if installed vertically, the support elements at the upper side of the spindle nut, whether leading or trailing, will always fall against the end face of the spindle nut, that is, they will fall downwardly.frictional retenion is undesirable since unreliable and subject to excessive wear and tear or contamination.